The present disclosure relates generally to an imaging module and an imaging reader for, and a method of, reading a target, such as a bar code symbol, to be electro-optically read by image capture over a field of view in a range of working distances away from the module/reader, and, more particularly, to using an aiming mark of an aiming light pattern to substantially center the target in the field of view, especially in a field crowded with targets, and, still more particularly, to enhancing the visibility of the aiming mark to serve as a more prominent visual indicator of a center zone of the field of view.
Solid-state imaging systems or imaging readers have long been used, in both handheld and hands-free modes of operation, in many industries, such as retail, manufacturing, warehousing, distribution, postal, transportation, logistics, etc., to electro-optically read targets, such as one- or two-dimensional bar code symbols to be decoded. A known imaging reader generally includes an imaging module that is mounted in a housing, and that has an aiming light system for projecting a visible aiming light pattern along an aiming axis to visually locate a target within a field of view and, thus, advise an operator which way the reader is to be moved in order to position the aiming light pattern on the target, typically at a center thereof, prior to reading; an illumination system for emitting illumination light toward the target for reflection and scattering therefrom; and an imaging system having a solid-state imager with a sensor array of photocells or light sensors, and an optical assembly for capturing return illumination light scattered and/or reflected from the target being imaged over the field of view centered on an imaging axis, and for projecting the captured illumination light onto the imager to initiate capture of an image of the target. The imager produces electrical signals that are decoded and/or processed by a programmed microprocessor or controller into information related to the target being read, e.g., decoded data identifying the target. The controller is operative for transmitting the decoded data, either via a wireless or wired link, to a remote host for further processing, e.g., price retrieval from a price database to obtain a price for the identified target.
Low cost imagers with rolling shutters are sometimes used to minimize cost, but this advantageously dictates that the aiming system be physically offset horizontally away from the imaging system. This horizontal offset or parallax positions the aiming light pattern to be off-center relative to the imaging axis and off to one side of the reader, and is especially undesirable when targets in the near range close to the reader are to be read, because the operator would be erroneously guided to position the reader such that a part of the target would typically lie outside the field of view, and therefore, the target will often not be centered and read.
It is known to configure the aiming light system in the imaging reader with a laser, a focusing lens, and a pattern shaping optical element, such as a diffractive optical element (DOE), or a refractive optical element (ROE) to project the aiming light pattern as, for example, a pair of crosshairs for placement at the center of the target, or as continuous lines or rows of light spots, for placement on the target to approximately indicate the field of view. Yet, the lasers and the optical components of such laser-based aiming systems are relatively expensive to fabricate and be optically aligned when mounted in the reader, thereby making them unsuitable for low cost, imaging readers. It is also known to configure the aiming light system in the imaging reader with one or more light emitting diodes (LEDs) to project the aiming light pattern as, for example, one or more generally circular spots, or as a single aiming line, for placement on the target. Such aiming light patterns generally indicate approximately where the center of the field of view is, or indicate approximately where the outer boundaries or end limits of the field of view are, but not both simultaneously. In any event, such laser-based and LED-based aiming systems are subject to the same aforementioned horizontal offset positioning error when the imaging and aiming light systems are offset from each other.
It is also known to project onto the target an aiming light pattern having a pair of aiming lines, each with a predetermined brightness, and having linear end portions that partially overlap each other to form an aiming mark having a brightness greater than the predetermined brightness to visually indicate the approximate center zone of the field of view over the range of working distances. Although generally satisfactory for its intended purpose, experience has shown that the aiming mark is not always clear and discernible in all cases, and is not always very visible or sufficiently bright when viewed, for example, against white backgrounds, and/or in brightly lit venues, and/or when text or bar code symbols are introduced into the field of view. Failure to accurately center a target is particularly important when the field of view is crowded with targets, for example, when multiple targets are located closely adjacent one another in a picklist from which warehouse personnel must select and read only those targets corresponding to ordered items that are to be retrieved from a warehouse or like facility.
Accordingly, it would be desirable to more accurately and more prominently indicate the center of the field of view of an imaging reader over a range of working distances despite a horizontal offset between the imaging and aiming light systems of the reader.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The module, reader and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.